Monoazo dichroic dye compound, polarizing plate composition comprising same, polarizing plate formed therefrom, and optical device comprising same

ABSTRACT

Disclosed is a mono-azo dichroic dye compound represented by the following Chemical Formula 1, a composition for polarizing plate, a polarizing plate, and an optical device. 
     
       
         
         
             
             
         
       
     
     In Chemical Formula 1, Z represents any one selected from the group consisting of CN, COOR 11 , indanone and 1,3-dioxoindane, wherein R 11  is any one selected from the group consisting of alkyl groups, aryl groups, and substituted or non-substituted heteroaryl groups. The mono-azo dichroic dye compound shows excellent dichroic properties, and has excellent heat resistance and photo-resistance, and thus may be used advantageously for a dye-based polarizing plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase entry pursuant to 35 U.S.C. § 371of International Application No. PCT/KR2021/009139, filed on Jul. 15,2021, and claims the benefit of and priority to Korean PatentApplication No. 10-2020-0182531, filed on Dec. 23, 2020, the disclosuresof which are incorporated by reference in their entirety for allpurposes as if fully set forth herein.

TECHNICAL FIELD

The present disclosure relates to a dichroic dye compound combined witha liquid crystal compound to form a polarizing plate, a composition fora polarizing plate including the same, a polarizing plate formedtherefrom, and an optical device including the same.

BACKGROUND

Optical devices, such as a liquid crystal display or an organic lightemitting diode, uses a polarizing plate to control optical activity orbirefringence property, or to prevent reflection of external light.

Polarizing plates used typically include a polarizing plate includingiodine as a polarizing substance, adsorbed to and aligned on apolarizing plate substrate made of polyvinyl alcohol or a derivativethereof, or a polarizing plate formed by combining a dichroic dye with aliquid crystal compound.

An iodine-based polarizing plate using iodine as a polarizing plate(polarizing element) shows excellent initial polarizing property in thevisible light region but shows significantly low polarizing property inthe near ultraviolet ray region. Moreover, such a polarizing plate isliable to water and heat, and shows a problem in terms of durability,when being used under a high-temperature and high-humidity condition fora long time.

A dye-based polarizing plate using a dichroic dye as a polarizingsubstance generally has higher durability under a high-temperature andhigh-humidity condition, as compared to an iodine-based polarizingplate, and thus is used for a part requiring high heat resistance anddurability, such as a car dashboard, an airplane, a liquid crystalprojector, etc. However, such a polarizing plate also has limited heatresistance and durability depending on dye and polymer materials usedtherefor.

Meanwhile, a bis-azo dye compound used as a polarizing substance for adye-based polarizing plate requires a complicated synthesis process andshows a low yield undesirably.

The background description provided herein is for the purpose ofgenerally presenting context of the disclosure. Unless otherwiseindicated herein, the materials described in this section are not priorart to the claims in this application and are not admitted to be priorart, or suggestions of the prior art, by inclusion in this section.

DISCLOSURE Technical Problem

The present disclosure is directed to providing a mono-azo dichroic dyecompound which has excellent dichroic properties and high heatresistance and photo-resistance, and thus may be used advantageously fora dye-based polarizing plate.

The present disclosure is also directed to providing a composition for apolarizing plate which has the above-mentioned characteristics, and apolarizing plate formed therefrom.

In addition, the present disclosure is directed to providing an opticaldevice including the polarizing plate having the above-mentionedcharacteristics.

Technical Solution

According to the first embodiment of the present disclosure, there isprovided a mono-azo dichroic dye compound represented by the followingChemical Formula 1:

-   -   wherein each of R₁ and R₂ independently represents any one        selected from the group consisting of: any one selected from        substituted or non-substituted aryl groups having 1-20 carbon        atoms, substituted or non-substituted heteroaryl groups having        1-20 carbon atoms, and substituted or non-substituted alkyl        groups having 1-20 carbon atoms; NR₄OH; NHR₅; NR₆; OR₇; COOR₈;        OCOR₉; SR₁₀; halogen groups; OH; CN; COOH; PO₃; SO₃; and NO₂        (wherein each of R₄-R₁₀ has 1-20 carbon atoms, and independently        represents any one selected from the group consisting of: any        one selected from H, alkoxy groups and alkoxyalkyl groups; any        one of halogen atoms and halogen-containing alkyl groups; and        any one selected from heterocyclic groups and aryl groups,        non-substituted or substituted with at least one selected from        the group consisting of alkoxy groups, alkoxyalkyl groups,        halogens and alkyl groups);    -   R₃ independently represents any one selected from the group        consisting of: H; any one selected from substituted or        non-substituted aryl groups having 1-20 carbon atoms,        substituted or non-substituted heteroaryl groups having 1-20        carbon atoms, and substituted or non-substituted alkyl groups        having 1-20 carbon atoms; NR₄OH; NHR₅; NR₆; OR₇; COOR₈; OCOR₉;        SR₁₀; halogen groups; OH; CN; COOH; PO₃; SO₃; and NO₂ (wherein        each of R₄-R₁₀ has 1-20 carbon atoms, and independently        represents any one selected from the group consisting of: any        one selected from H, alkoxy groups and alkoxyalkyl groups; any        one of halogen atoms and halogen-containing alkyl groups; and        any one selected from heterocyclic groups and aryl groups,        non-substituted or substituted with at least one selected from        the group consisting of alkoxy groups, alkoxyalkyl groups,        halogens and alkyl groups);    -   each of X₁ and X₂ independently represents any one selected from        the group consisting of N, S, O and C;    -   each of Y₁ and Y₂ independently represents any one selected from        the group consisting of C, S, O and N; and    -   Z represents any one selected from the group consisting of CN,        COOR₁₁, indanone and 1,3-dioxoindane, wherein R₁₁ is any one        selected from the group consisting of alkyl groups, aryl groups        and substituted or non-substituted heteroaryl groups.

According to the second embodiment of the present disclosure, there isprovided the mono-azo dichroic dye compound as defined in the firstembodiment, each of R₁ and R₂ independently represents any one selectedfrom the group consisting of CN, OH, NHR₅, NR₆, OR₇ and COOR₈, and R₃independently represents any one selected from the group consisting ofH, CN, OH, NHR₅, NR₆, OR₇ and COOR₈. Particularly, each of R₁ and R₂ maybe any one selected from the group consisting of NHR₅, NR₆, OR₇ andCOOR₈. More particularly, R₁ may be NR₆ or OR₇, and R₂ may be OR₇ orCOOR₈, and R₃ is H.

According to the third embodiment of the present disclosure, there isprovided the mono-azo dichroic dye compound as defined in the first orthe second embodiment, wherein each of X₁ and X₂ is independentlyselected from N and C.

According to the fourth embodiment of the present disclosure, there isprovided the mono-azo dichroic dye compound as defined in any one of thefirst to the third embodiments, wherein each of Y₁ and Y₂ isindependently selected from S and O.

According to the fifth embodiment of the present disclosure, there isprovided the mono-azo dichroic dye compound as defined in any one of thefirst to the fourth embodiments, wherein Z is selected from CN, indanoneand 1,3-dioxoindane. Particularly, Z may be CN or indanone.

In another aspect of the present disclosure, there are provided acomposition for a polarizing plate including the mono-azo dichroic dyecompound as defined in any one of the first to the fifth embodiments incombination with a liquid crystal compound, and a polarizing plateformed by curing the composition. The polarizing plate may have adichroic ratio (D0) of 20-24, a heat resistance (Δintensity) of 4% orless, and a photo-resistance (Δintensity) of 4% or less.

In still another aspect of the present disclosure, there is provided anoptical device including the polarizing plate.

Advantageous Effects

The dichroic dye compound according to the present disclosure is amono-azo typed dichroic dye compound represented by Chemical Formula 1,shows excellent dichroic properties, and has excellent heat resistanceand photo-resistance. Therefore, the dichroic dye compound shows highdurability, even when being prepared or used under a severe condition.

In addition, the mono-azo typed dichroic dye compound is synthesizedmore easily with a higher yield, as compared to a bis-azo typed dichroicdye compound.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Priorto the description, it should be understood that the terms used in thespecification and the appended claims should not be construed as limitedto general and dictionary meanings, but interpreted based on themeanings and concepts corresponding to technical aspects of the presentdisclosure on the basis of the principle that the inventor is allowed todefine terms appropriately for the best explanation.

The mono-azo dichroic dye compound according to the present disclosureis represented by the following Chemical Formula 1, and is a mono-azotype compound having an azo group only at one side.

-   -   wherein each of R₁ and R₂ independently represents any one        selected from the group consisting of: any one selected from        substituted or non-substituted aryl groups having 1-20 carbon        atoms, substituted or non-substituted heteroaryl groups having        1-20 carbon atoms, and substituted or non-substituted alkyl        groups having 1-20 carbon atoms; NR₄OH; NHR₅; NR₆; OR₇; COOR₈;        OCOR₉; SR₁₀; halogen groups; OH; CN; COOH; PO₃; SO₃; and NO₂        (wherein each of R₄-R₁₀ has 1-20 carbon atoms, and independently        represents any one selected from the group consisting of: any        one selected from H, alkoxy groups and alkoxyalkyl groups; any        one of halogen atoms and halogen-containing alkyl groups; and        any one selected from heterocyclic groups and aryl groups,        non-substituted or substituted with at least one selected from        the group consisting of alkoxy groups, alkoxyalkyl groups,        halogens and alkyl groups);    -   R₃ independently represents any one selected from the group        consisting of: H; any one selected from substituted or        non-substituted aryl groups having 1-20 carbon atoms,        substituted or non-substituted heteroaryl groups having 1-20        carbon atoms, and substituted or non-substituted alkyl groups        having 1-20 carbon atoms; NR₄OH; NHR₅; NR₆; OR₇; COOR₈; OCOR₉;        SR₁₀; halogen groups; OH; CN; COOH; PO₃; SO₃; and NO₂ (wherein        each of R₄-R₁₀ has 1-20 carbon atoms, and independently        represents any one selected from the group consisting of: any        one selected from H, alkoxy groups and alkoxyalkyl groups; any        one of halogen atoms and halogen-containing alkyl groups; and        any one selected from heterocyclic groups and aryl groups,        non-substituted or substituted with at least one selected from        the group consisting of alkoxy groups, alkoxyalkyl groups,        halogens and alkyl groups);    -   each of X₁ and X₂ independently represents any one selected from        the group consisting of N, S, O and C;    -   each of Y₁ and Y₂ independently represents any one selected from        the group consisting of C, S, O and N; and    -   Z represents any one selected from the group consisting of CN,        COOR₁₁, indanone and 1,3-dioxoindane, wherein R₁₁ is any one        selected from the group consisting of alkyl groups, aryl groups        and substituted or non-substituted heteroaryl groups.

As described above, it is known that a bis-azo typed dichroic dyecompound requires a complicated synthesis process and shows asignificantly low yield. The dichroic dye compound according to thepresent disclosure is a mono-azo typed compound, and thus is obtainedthrough a relatively simple synthesis process with an improved yield. Inaddition, even though the dichroic compound is a mono-azo typedcompound, it shows excellent dichroic properties, and has high heatresistance and photo-resistance.

[R₁, R₂ and R₃ in Chemical Formula 1]

-   -   wherein each of R₁ and R₂ independently represents any one        selected from the group consisting of: any one selected from        substituted or non-substituted aryl groups having 1-20 carbon        atoms, substituted or non-substituted heteroaryl groups having        1-20 carbon atoms, and substituted or non-substituted alkyl        groups having 1-20 carbon atoms; NR₄OH; NHR₅; NR₆; OR₇; COOR₈;        OCOR₉; SR₁₀; halogen groups; OH; CN; COOH; PO₃; SO₃; and NO₂        (wherein each of R₄-R₁₀ has 1-20 carbon atoms, and independently        represents any one selected from the group consisting of: any        one selected from H, alkoxy groups and alkoxyalkyl groups; any        one of halogen atoms and halogen-containing alkyl groups; and        any one selected from heterocyclic groups and aryl groups,        non-substituted or substituted with at least one selected from        the group consisting of alkoxy groups, alkoxyalkyl groups,        halogens and alkyl groups); and    -   R₃ independently represents any one selected from the group        consisting of: H; any one selected from substituted or        non-substituted aryl groups having 1-20 carbon atoms,        substituted or non-substituted heteroaryl groups having 1-20        carbon atoms, and substituted or non-substituted alkyl groups        having 1-20 carbon atoms; NR₄OH; NHR₅; NR₆; OR₇; COOR₈; OCOR₉;        SR₁₀; halogen groups; OH; CN; COOH; PO₃; SO₃; and NO₂ (wherein        each of R₄-R₁₀ has 1-20 carbon atoms, and independently        represents any one selected from the group consisting of: any        one selected from H, alkoxy groups and alkoxyalkyl groups; any        one of halogen atoms and halogen-containing alkyl groups; and        any one selected from heterocyclic groups and aryl groups,        non-substituted or substituted with at least one selected from        the group consisting of alkoxy groups, alkoxyalkyl groups,        halogens and alkyl groups).

In the expression ‘substituted or non-substituted aryl groups having1-20 carbon atoms, substituted or non-substituted heteroaryl groupshaving 1-20 carbon atoms, and substituted or non-substituted alkylgroups having 1-20 carbon atoms’ used to define R₁, R₂ and R₃, the term‘substituted’ refers to substitution of an aryl, heteroaryl or alkylgroups with at least one substituent selected from the group consistingof alkoxy, alkoxyalkyl, halogen and alkyl groups, or the like.

Particularly, each of R₁ and R₂ may independently represent any oneselected from the group consisting of CN, OH, NHR₅, NR₆, OR₇ and COOR₈,and R₃ independently represents any one selected from the groupconsisting of H, CN, OH, NHR₅, NR₆, OR₇ and COOR₈.

More particularly, each of R₁ and R₂ may be any one selected from thegroup consisting of NHR₅, NR₆, OR₇ and COOR₈.

Most particularly, R₁ may be NR₆ or OR₇, and R₂ may be OR₇ or COOR₈, andR₃ is H.

[X₁ and X₂ in Chemical Formula 1]

Each of X₁ and X₂ independently represents any one selected from thegroup consisting of N, S, O and C.

More particularly, each of X₁ and X₂ may be independently selected fromN and C.

[Y₁ and Y₂ in Chemical Formula 1]

Each of Y₁ and Y₂ independently represents any one selected from thegroup consisting of C, S, O and N.

More particularly, each of Y₁ and Y₂ may be independently selected fromS and O.

[Z in Chemical Formula 1]

Z represents any one selected from the group consisting of CN, COOR₁₁,indanone and 1,3-dioxoindane, wherein R₁₁ is any one selected from thegroup consisting of alkyl groups, aryl groups, and substituted ornon-substituted heteroaryl groups. Any one of the above-mentioned groupsas Z contributes to improvement of the heat resistance of the mono-azodichroic dye compound represented by Chemical Formula 1. For example,R₁₁ may have 1-15 carbon atoms, particularly 1-10 carbon atoms.

Particularly, Z may be selected from the group consisting of CN,indanone and 1,3-dioxoindane. More particularly, Z may be CN orindanone.

Most particularly, the mono-azo dichroic dye compound of ChemicalFormula 1 may be any one selected from the compounds represented by thefollowing chemical formulae:

The mono-azo dichroic compound of Chemical Formula 1 may be synthesizedthrough a combination of known organic chemical synthesis processes.

For example, the mono-azo dichroic compound may be synthesized by usinga known method with reference to a textbook, such as Dichroic Dyes forLiquid Crystal Display (A. V. lvashchenko, CRC, 1994).

The mono-azo dichroic dye compound according to the present disclosureis combined with a liquid crystal compound to form a composition for apolarizing plate, and the composition is cured to form a polarizingplate. In other words, it is possible to align the mono-azo dichroic dyecompound with a high degree of alignment by combining the dichroic dyecompound with a liquid crystal compound, while inhibiting deposition ofthe dichroic dye compound.

Any known low-molecular weight liquid crystal compound and polymericliquid crystal compound may be used as a liquid crystal compoundcontained in the composition for a polarizing plate according to thepresent disclosure. Herein, ‘low-molecular weight liquid crystalcompound’ refers to a liquid crystal compound having no repeating unitin its chemical structure. In addition, ‘polymeric liquid crystalcompound’ refers to a liquid crystal compound having repeating units inits chemical structure. For example, a curable liquid crystal compoundmay be used in order to improve the alignability of a dichroic dyecompound and particular examples of such a liquid crystal compoundinclude 4-(3-acryloyloxypropoxy)benzoic acid o-tolyl ester, or the like.

In the composition for a polarizing plate according to the presentdisclosure, the mono-azo dichroic dye compound represented by ChemicalFormula 1 may be used in an amount of 2-40 wt % based on the totalweight of the solid content of the composition, but is not limitedthereto.

When preparing the composition for a polarizing plate, a mixture of adichroic dye showing a red color, a dichroic dye showing a blue colorand a dichroic dye showing a green color, or a dichroic dye having astructure realizing dichroism showing a red color, a structure realizingdichroism showing a blue color and a structure realizing dichroismshowing a green color may be added, if necessary. The polarizing plateusing such a mixture of dichroic dyes may perform linear polarizationtotally in the visible light region. In addition, in order to carry outcolor compensation, a dichroic dye showing any color other than red,green and blue, or a dichroic dye including a structure realizingdichroism showing any color other than red, green and blue may be addedto the composition for a polarizing plate. When dichroic dyes for a redcolor, blue color and a green color and a dichroic dye for colorcompensation are used, they may be combined at any ratio depending ontheir absorption wavelengths and the ratio is not particularly limited.

Particular examples of other additives include, but are not limited to:a catalyst, a sensitizer, a stabilizer, a chain transfer agent, aninhibitor, an accelerator, a surfactant, a lubricant, a wetting agent, adispersant, a hydrophobicity-imparting agent, an adhesive, a flowenhancer, an anti-foaming agent, a diluent, a colorant, a dye, apigment, etc. generally known to those skilled in the art. Suchingredients may be selected and combined suitably, as necessary.

In addition, the composition for a polarizing plate may include 1-10parts by weight, particularly 2-7 parts by weight of a curing agent, ifnecessary. In other words, when the composition for a polarizing plateis coated on a substrate and a polarizing plate is formed, it is notrequired to add any separate curing agent to the composition for apolarizing plate in the case of curing using electron beams. However,when the composition for a polarizing plate requires drying in the caseof photocuring or thermal curing after the coating, a separate curingagent is added to the composition for a polarizing plate.

Any curing agent used conventionally in the art may be used. Particularexamples of a photopolymerization initiator using ultraviolet raysinclude at least one selected from the group consisting of at least oneactive halogen compound selected from halomethyloxadiazole compounds andhalomethyl-s-triazine compounds, 3-aryl substituted coumarin compounds,benzophenone compounds, acetophenone compounds and derivatives thereof,cyclopentadiene-benzene-iron complexes and salts thereof, and oximecompounds. Particular examples of the active halogen compound, which isa halomethyloxadiazole compound, include2-halomethyl-5-vinyl-1,3,4-oxadiazole compounds,2-trichloromethyl-5-styryl-1,3,4-oxadiazole,2-trichloromethyl-5-(p-cyanostyryl)-1,3,4-oxadiazole,2-trichloromethyl-5-(p-methoxystyryl)-2,3,4-oxadiazole, or the like.Particular examples of the active halogen compound, which is ahalomethyl-s-triazine compound, include vinyl-halomethyl-s-triazinecompounds, 2-(naphtho-1-yl)-4,6-bis-halomethyl-s-triazine compound and4-(p-aminophenyl)-2,6-di-halomethyl-s-triazine compound, or the like.

Particular examples of the photoinitiator include Irgacure series (e.g.Irgacure 651, Irgacure 184, Irgacure 500, Irgacure 1000, Irgacure 149,Irgacure 819, Irgacure 261) and Darocure series (e.g. Darocure 1173)available from Ciba Specialty Chemicals,4,4′-bis(diethylamino)-benzophenone,2-(O-benzoyloxime)-1-[4-(phenylthiol)phenyl]-1,2-octanedione,1-(0-acetyloxime)-1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone,2-benzyl-2-dimethylamino-4-morpholinobutyrophenone,2,2-dimethoxy-2-phenylacetophenone,2-(o-chlorophenyl)-4,5-diphenylimidazolyl dimer,2-(o-fluorophenyl)-4,5-diphenylimidazolyl dimer,2-(o-methoxyphenyl)-4,5-diphenylimidazolyl dimer,2-(p-methoxyphenyl)-4,5-diphenylimidazolyl dimer,2-(p-dimethoxyphenyl)-4,5-diphenylimidazolyl dimer,2-(2,4-dimethoxyphenyl)-4,5-diphenylimidazolyl dimer,2-(p-mercaptophenyl)-4,5-diphenylimidazolyl dimer, benzoin isopropylether, or the like. Such curing agents may be used alone or incombination.

To carry out coating with the composition for a polarizing plate, asuitable solvent may be selected and used for combining the ingredients,including the mono-azo dichroic dye compound, with one another. Thesolvent and solid content in the composition are not particularlylimited, but may be selected and used by those skilled in the art tomeet the objects of the present disclosure.

The substrate coated with the composition for a polarizing plate to forma polarizing plate may be a glass plate or plastic substrate. Particularexamples of the plastic substrate include but are not limited to thosemade of acrylic resin, polycarbonate resin, epoxy resin or polyesterresin.

The composition for a polarizing plate may be applied to the substratethrough a thin film coating process used currently in the art, such asspin coating, blade coating, casting coating or roll coating. Thecomposition for a polarizing plate may be coated so that the finallycured polarizing plate may have a thickness of 0.1-10 micrometers,particularly 0.3-7 micrometers, but is not limited thereto. When curingthe composition for a polarizing plate after the coating, a known curingprocess, such as electron beam curing, thermal curing or UV curing, maybe used, but the curing process is not particularly limited.

Meanwhile, when the polarizing plate obtained by using a dichroic dye isused for a liquid crystal display (LCD), the alignability of the coateddichroic dye is regarded as important. Therefore, the substrate itselfmay be provided with alignability or a separate aligning film may beformed to impart alignability to the substrate in order to improve thealignability of the dichroic dye, before coating the polarizing plateusing the composition for a polarizing plate.

The alignability to the substrate may be obtained by forming surfaceirregularities on the surface of the substrate to impart orientabilityto the molecules forming the coating film. In addition, a method forimparting alignability to the substrate may be used, the methodincluding: forming a separate aligning film formed of an azo-basedcompound, polyimide, polyamide, cinnamate or amic acid on the substrate,and subjecting the aligning film to a rubbing or photo-alignment processto impart alignability. As a non-contact surface treatment method, aphoto-alignment method may also be used, the method includingirradiating polarized UV rays to the polarizing plate to impartanisotropic property to the coating film.

If necessary, the surface of the polarizing plate formed by using themono-azo dichroic dye compound according to the present disclosure maybe subjected to post-treatment through antistatic treatment, coronatreatment, hard coating treatment, antireflection treatment, antiglaretreatment, or the like.

The polarizing plate obtained by the above-described method has a highdichroic ratio, shows excellent durability, such as heat resistance andphoto-resistance, under a high-temperature and high-humidity condition,and causes little discoloration or degradation of polarizability, andthus may be used for optical devices, such as car dash boards, airplanesand liquid crystal projectors, requiring high heat resistance,durability and polarizability. The polarizing plate may have a dichroicratio (D0) of 20-24, a heat resistance (Δintensity) of 4% or less, and aphoto-resistance (Δintensity) of 4% or less. Herein, each of thedichroic ratio (D0), heat resistance (Δintensity) and thephoto-resistance (Δintensity) of the polarizing plate means the valuedetermined by each of the evaluation methods as defined in the followingparts of ‘Evaluation of Dichroic Ratio’, ‘Evaluation of Heat Resistance’and ‘Evaluation of Photo-resistance’.

Hereinafter, the present disclosure will be explained in more detailwith reference to exemplary embodiments. This disclosure may, however,be embodied in many different forms and should not be construed aslimited to the exemplary embodiments set forth therein. It will beapparent that these exemplary embodiments are provided so that thepresent disclosure will be complete and understood easily by thoseskilled in the art.

<Determination of Compound Structure>

The structure of a compound was determined by using a LC massspectrometer. A compound to be determined was dissolved in THF and usedfor determination. The peaks were analyzed to determine the m/z value.

<Evaluation of Photo-Resistance>

Photo-resistance was evaluated by exposing each of the polarizing platesaccording to Examples and Comparative Examples to Redlenser Flash LEDLENSER P7R(9408R) at 1000 lm for 1 hour and measuring absorbance.Herein, photo-resistance was evaluated from a difference between theinitial absorbance and the absorbance after exposure.

Photo-resistance (ΔIntensity)=[(Absorbance after exposure at 1000 lm for1 hour)−(Initial absorbance)]×100(%)

<Evaluation of Heat Resistance>

Heat resistance was evaluated from a difference between the initialabsorbance and the absorbance determined after allowing each of thepolarizing plates according to Examples and Comparative Examples tostand in a constant-temperature and constant-humidity system at 80° C.for 250 hours.

Heat resistance (ΔIntensity)=[(Absorbance after 250 hours)−(Initialabsorbance)]×100(%)

<Evaluation of Dichroic Ratio>

The dichroic ratio was calculated according to the following formula,after measuring the absorbance of each of the polarizing platesaccording to Examples and Comparative Examples in a wavelength range of550-700 nm by using a multichannel spectrometer, while a linearpolarizer was inserted to the light source side of an opticalmicroscope.

Dichroic ratio (D0)=Az0/Ay0

-   -   wherein Az0 represents the absorbance to the polarized light in        the direction of absorption axis of a light-absorbing polarizing        plate, and Zy0 represents the absorbance in the direction of        polarization axis of the polarizing plate.

Synthesis Examples Synthesis of Intermediate 1-1

First, phosphoryl trichloride (1.27 g, 8.3 mmol) was added dropwisegradually to 10 mL of dimethyl formamide (DMF) at 0° C. under nitrogenatmosphere, and the resultant mixture was agitated for 1 hour. Next,thieno[2,3-d]thiazol-2-amine (1 g, 6.4 mmol) was introduced thereto andthe resultant mixture was warmed to 80° C. and agitated to carry outreaction. Then, the resultant mixture was cooled to room temperature and30 mL of water was added thereto to quench the reaction. Afterintroducing 30 mL of 1 N NaOH to the resultant solid, 50 mL ofchloroform was further introduced and dissolved. Then, the resultantproduct was washed twice with water, the organic layer was separated,dry magnesium sulfate was added thereto, the resultant product wasagitated and filtered, and the filtrate was distilled under reducedpressure. The concentrated compound was purified through a silica columnby using chloroform and ethyl acetate to obtain solid intermediate 1-1(0.91 g, 77%, MS: [M+H]+=184.0).

Synthesis of Intermediate 1-2

Intermediate 1-1 (1 g, 5.4 mmol) was introduced to 3 mL of acetic acidand 7 mL of propionic acid at 0° C., and the resultant mixture wasagitated for 30 minutes. Next, sodium nitrite (0.39 g, 5.7 mmol) wasdissolved in 16 mL of sulfuric acid and added dropwise graduallythereto, and the resultant mixture was agitated for 30 minutes, whilemaintaining the temperature at 5° C. or lower. N,N-diethylaniline (1.2g, 8.1 mmol) was dissolved in 5 mL of methanol and added dropwisegradually thereto, and the resultant mixture was agitated for 2 hours.Herein, the reaction mixture was titrated with 2 N aqueous sodiumacetate solution to maintain pH 5-7. After completing the reaction, themixture was filtered and washed twice with water and methanol to obtainsolid intermediate 1-2 (1.4 g, 75%, MS: [M+H]+=345.1).

Synthesis Example 1

Intermediate 1-2 (0.5 g, 1.5 mmol) and 2-(4-buthoxyphenyl)acetonitrile(0.33 g, 1.7 mmol) were dissolved in 10 mL of ethanol. Next, 5 mol % ofpiperidine was added thereto and the resultant mixture was refluxed for2 hours. The reaction mixture was cooled to room temperature and theresultant solid was extracted with 20 mL of chloroform and 20 mL ofwater three times. Then, the resultant product was dried with magnesiumsulfate, the solvent was evaporated, and the product was purifiedthrough a silica column by using chloroform and ethyl acetate to obtainCompound 1 (0.45 g, 60%, MS: [M+H]+=515.3).

Synthesis Example 2

Compound 2 (0.45 g, 57%, MS: [M+H]+=543.8) was obtained in the samemanner as Synthesis Example 1, except that2-(4-(hexyloxy)phenyl)acetonitrile was used instead of2-(4-butoxyphenyl)acetonitrile.

Synthesis Example 3

Compound 3 (1.2 g, 66%, MS: [M+H]⁺=629.4) was obtained in the samemanner as Synthesis Example 1, except that2-(4-((11-hydroxyundecyl)oxy)phenyl)acetonitrile was used instead of2-(4-butoxyphenyl)acetonitrile.

Synthesis Example 4

Compound 3 (0.5 g, 0.8 mmol) obtained according to Synthesis Example 3and methacrylic anhydride (0.15 g, 0.95 mmol) were dissolved in 30 mL ofchloroform. Next, 10 mol % of BHT, 1.1 equivalent of TEA and 5 mol % ofDMAP were introduced to the mixed solution and the resultant mixture wasagitated at room temperature for 5 hours. After quenching the reactionwith aqueous ammonium chloride solution, the resultant product wasextracted with 30 mL of chloroform and 30 mL of water three times. Afterdrying the resultant product with magnesium sulfate and evaporating thesolvent, the resultant product was purified through a silica column byusing chloroform and ethyl acetate to obtain Compound 4 (0.39 g, 70%,MS: [M+H]⁺=697.3).

Synthesis Example 5

Compound 5 (0.38 g, 51%, MS: [M+H]⁺=501.9) was obtained in the samemanner as Synthesis Example 1, except that ethyl 4-(cyanomethyl)benzoatewas used instead of 2-(4-butoxyphenyl)acetonitrile.

Synthesis of Intermediate 6-1

Intermediate 1-2 (0.5 g, 1.5 mmol) and 2-cyanoacetic acid (0.15 g, 1.7mmol) were dissolved in 20 mL of toluene. After adding 5 mol % of aceticacid to the mixed solution, the resultant mixture was refluxed for 1day. The reaction mixture was cooled to room temperature, and theresultant solid was filtered and washed with 50 mL of ethanol to obtainIntermediate 6-1 (0.29 g, 81%, MS: [M+H]⁺=411.2).

Synthesis Example 6

At 0° C., Intermediate 6-1 (0.5 g, 5.9 mmol) and 4-hexylphenol (1.1 g,6.5 mmol) were dissolved in 50 mL of chloroform. After adding DMAP (0.07g, 0.58 mmol) and EDC (1.0 g, 6.4 mmol) thereto, the resultant mixturewas warmed to room temperature and agitated. After quenching thereaction with aqueous ammonium chloride solution, the resultant productwas extracted with 20 mL of chloroform three times and dried withmagnesium sulfate, and the concentrated compound was purified through asilica column by using chloroform and ethyl acetate to obtain Compound 6(0.8 g, 55%, MS: [M+H]⁺=571.3).

Synthesis Example 7

Compound 7 (1.2 g, 66%, MS: [M+H]⁺=587.7) was obtained in the samemanner as Synthesis Example 6, except that butyl-4-hydroxybenzoate wasused instead of 4-hexylphenol.

Synthesis of Intermediate 8-1

Intermediate 8-1 (1.5 g, 69%, MS: [M+H]⁺=399.0) was obtained in the samemanner as Synthesis of Intermediate 1-2, except that 1-hexylindoline wasused instead of N,N-diethylaniline.

Synthesis Example 8

Compound 8 (0.42 g, 56%, MS: [M+H]⁺=547.3) was obtained in the samemanner as Synthesis Example 1, except that2-(4-(hexyloxy)phenyl)acetonitrile was used instead of2-(4-butoxyphenyl)acetonitrile and Intermediate 8-1 was used instead ofIntermediate 1-2.

Synthesis of Intermediate 9-1

Intermediate 9-1 (0.37 g, 63%, MS: [M+H]⁺=466.0) was obtained in thesame manner as Synthesis of Intermediate 6-1, except that Intermediate8-1 was used instead of Intermediate 1-2.

Synthesis Example 9

Compound 9 (0.28 g, 53%, MS: [M+H]⁺=642.1) was obtained in the samemanner as Synthesis Example 7, except that Intermediate 9-1 was usedinstead of Intermediate 6-1.

Synthesis Example 10

Compound 10 (0.33 g, 49%, MS: [M+H]⁺=625.3) was obtained in the samemanner as Synthesis Example 6, except that Intermediate 9-1 was usedinstead of Intermediate 6-1.

Synthesis Example 11

First, 4-butylaniline (2 g, 13.4 mmol) was added to 10 mL ofhydrochloric acid, 5 mL of aqueous sodium nitrite solution (1.017 g,14.7 mmol) was added dropwise thereto, and the resultant mixture wasagitated for 30 minutes. Next, 0.08 g of sulfamic acid was added theretoand the resultant mixture was further agitated for 30 minutes.Thieno[2,3-d]thiazol-2-amine (0.3 g, 6.7 mmol) was dissolved in 10 mL ofmethanol and the resultant solution was added dropwise gradually, andthen the resultant mixture was agitated for 2 hours. After completingthe reaction, the resultant product was washed with 30 mL of methanoland 30 mL of water and filtered to obtain Intermediate A-1. Then, solidCompound A (0.28 g, 37%, MS: [M+H]⁺=476.2) was obtained in the samemanner as Synthesis of Intermediate 1-2, except that Intermediate A-1was used instead of Intermediate 1-1.

Synthesis Example 12

First, 2-amino-4-chlorothiazol-5-carboaldehyde (2 g, 12.3 mmol) wasadded to 10 mL of sulfuric acid and 5 mL of aqueous sulfuric acidsolution of sodium nitrite (1.018 g, 14.8 mmol) was added dropwisethereto, and the resultant mixture was agitated for 30 minutes. Next,0.08 g of sulfamic acid was further introduced thereto and the resultantmixture was further agitated for 30 minutes. Then, N,N-diethylaniline(1.1 g, 7.4 mmol) was dissolved in 10 mL of methanol and the resultantsolution was added dropwise gradually, and the resultant mixture wasagitated for 2 hours. After completing the reaction, the resultantproduct was washed with 30 mL of methanol and 30 mL of water andfiltered to obtain Intermediate B-1. Then, solid Compound B (1.33 g,83%, MS: [M+H]⁺=521.2) was obtained in the same manner as SynthesisExample 2, except that Intermediate B-1 was used instead of Intermediate1-2.

<Manufacture of Polarizing Plate>

Preparation Example 1

First, 2 wt % of an aligning layer-forming solution (prepared bydissolving 2 wt % of polyacrylate having methoxy cinnamate (MPN-Ci) as aphotosensitive functional group in the form of a branch in 98% ofcyclopentanone (CPO)) was spin-coated on a cycloolefin polymer (COP)film at 1000 rpm for 10 seconds, dried at 80° C. for 2 minutes, andcured with UVB at a dose of 250 mJ. A composition including the dichroicdye of Synthesis Example 1 according to the ingredients at the mixingratio as shown in the following Table 1 was dissolved in cyclopentanoneat room temperature to obtain a solution of composition for a polarizingplate having a solid content of 26 wt %. Since the composition included5 wt % of a curing agent in the reactive liquid crystal itself, anyseparate curing agent was not added to the composition.

TABLE 1 Content (parts by Composition for Polarizing Plate weight)Curable liquid crystal RSD-1 (Sundia Co., China) 75 RSM-1 (LG Chem.) 25Dichroic dye Synthesis Example 1 2.0 PI Irgacure 369 2.0 (Ciba SpecialtyChemicals) Surf. BYK-358N (BYK Co.) 1.0 Solvent Cyclopentanone

The composition for a polarizing plate was spin coated on the top of aphotoalignment-treated aligning layer at 1000 rpm for 30 seconds. Then,the spin coated polarizing film-forming composition was dried at 120° C.for 2 minutes. To carry out photo-crosslinking of the liquid crystal anddye ingredients, the coating layer was cured with a UVB lamp at 250 mJunder N₂ gas atmosphere. The cured polarizing plate film had a thicknessof 0.9 μm.

Preparation Example 2

A polarizing plate film was obtained in the same manner as PreparationExample 1, except that Compound 2 according to Synthesis Example 2 wasused instead of Compound 1 according to Synthesis Example 1.

Preparation Example 3

A polarizing plate film was obtained in the same manner as PreparationExample 1, except that Compound 3 according to Synthesis Example 3 wasused instead of Compound 1 according to Synthesis Example 1.

Preparation Example 4

A polarizing plate film was obtained in the same manner as PreparationExample 1, except that Compound 4 according to Synthesis Example 4 wasused instead of Compound 1 according to Synthesis Example 1.

Preparation Example 5

A polarizing plate film was obtained in the same manner as PreparationExample 1, except that Compound 5 according to Synthesis Example 5 wasused instead of Compound 1 according to Synthesis Example 1.

Preparation Example 6

A polarizing plate film was obtained in the same manner as PreparationExample 1, except that Compound 6 according to Synthesis Example 6 wasused instead of Compound 1 according to Synthesis Example 1.

Preparation Example 7

A polarizing plate film was obtained in the same manner as PreparationExample 1, except that Compound 7 according to Synthesis Example 7 wasused instead of Compound 1 according to Synthesis Example 1.

Preparation Example 8

A polarizing plate film was obtained in the same manner as PreparationExample 1, except that Compound 8 according to Synthesis Example 8 wasused instead of Compound 1 according to Synthesis Example 1.

Preparation Example 9

A polarizing plate film was obtained in the same manner as PreparationExample 1, except that Compound 9 according to Synthesis Example 9 wasused instead of Compound 1 according to Synthesis Example 1.

Preparation Example 10

A polarizing plate film was obtained in the same manner as PreparationExample 1, except that Compound 10 according to Synthesis Example 10 wasused instead of Compound 1 according to Synthesis Example 1.

Comparative Example 1

A polarizing plate film was obtained in the same manner as PreparationExample 1, except that Compound A according to Synthesis Example 11 wasused instead of Compound 1 according to Synthesis Example 1.

Comparative Example 2

A polarizing plate film was obtained in the same manner as PreparationExample 1, except that Compound B according to Synthesis Example 12 wasused instead of Compound 1 according to Synthesis Example 1.

Each of the polarizing plates were evaluated in terms of its dichroicratio, heat resistance and photo-resistance. The results are shown inthe following Table 2.

TABLE 2 Dichroic Heat resistance (Δ Photo-resistance (Δ ratio intensity)intensity) Prep. Ex. 1 20.77   2% 2.8% Prep. Ex. 2 19.75 2.8% 2.5% Prep.Ex. 3 22.38 1.9% 1.7% Prep. Ex. 4 19.88 2.2% 2.5% Prep. Ex. 5 22.25 1.8%1.5% Prep. Ex. 6 21.16 2.4% 2.0% Prep. Ex. 7 21.01 3.9% 2.0% Prep. Ex. 820.16 2.7% 1.9% Prep. Ex. 9 20.74 2.6% 2.6% Prep. Ex. 10 21.38 3.3% 2.7%Comp. Ex. 1 19.73   5%   3% Comp. Ex. 2 5.3 29.8%  24.1% 

It can be seen from Table 2 that the polarizing plates according toPreparation Examples of the present disclosure has an improved dichroicratio and excellent photo-resistance and heat resistance, as compared toComparative Examples.

1. A mono-azo dichroic dye compound represented by Chemical Formula 1:

wherein each of R₁ and R₂ independently represents any one selected from the group consisting of: substituted or non-substituted aryl groups having 1-20 carbon atoms, substituted or non-substituted heteroaryl groups having 1-20 carbon atoms, substituted or non-substituted alkyl groups having 1-20 carbon atoms, NR₄OH, NHR₅, NR₆, OR₇, COOR₈, OCOR₉, SR₁₀, halogen groups, OH, CN, COOH, PO₃, SO₃, and NO₂; wherein R₃ independently represents any one selected from the group consisting of: H, from substituted or non-substituted aryl groups having 1-20 carbon atoms, substituted or non-substituted heteroaryl groups having 1-20 carbon atoms, substituted or non-substituted alkyl groups having 1-20 carbon atoms, NR₄OH, NHR₅, NR₆, OR₇, COOR₈, OCOR₉, SR₁₀, halogen groups, OH, CN, COOH, PO₃, SO₃, and NO₂; wherein each of R₄-R₁₀ has 1-20 carbon atoms, and independently represents any one selected from the group consisting of: H, alkoxy groups, alkoxyalkyl groups, halogen atoms, halogen-containing alkyl groups, heterocyclic groups, aryl groups, non-substituted or substituted with at least one selected from the group consisting of alkoxy groups, alkoxyalkyl groups, halogens and alkyl groups; each of X₁ and X₂ independently represents any one selected from the group consisting of N, S, O and C; each of Y₁ and Y₂ independently represents any one selected from the group consisting of C, S, O and N; and Z represents any one selected from the group consisting of CN, COOR₁₁, indanone and 1,3-dioxoindane, wherein R₁₁ is any one selected from the group consisting of alkyl groups, aryl groups, and substituted or non-substituted heteroaryl groups.
 2. The mono-azo dichroic dye compound according to claim 1, wherein each of R₁ and R₂ independently represents any one selected from the group consisting of CN, OH, NHR₅, NR₆, OR₇ and COOR₈, and R₃ independently represents any one selected from the group consisting of H, CN, OH, NHR₅, NR₆, OR₇ and COOR₈.
 3. The mono-azo dichroic dye compound according to claim 1, wherein each of R₁ and R₂ independently represents any one selected from the group consisting of NHR₅, NR₆, OR₇ and COOR₈.
 4. The mono-azo dichroic dye compound according to claim 1, wherein R₁ is NR₆ or OR₇, and R₂ is OR₇ or COOR₈, and R₃ is H.
 5. The mono-azo dichroic dye compound according to claim 1, wherein each of X₁ and X₂ is independently selected from N and C.
 6. The mono-azo dichroic dye compound according to claim 1, wherein each of Y₁ and Y₂ is independently selected from S and O.
 7. The mono-azo dichroic dye compound according to claim 1, wherein Z is selected from CN, indanone and 1,3-dioxoindane.
 8. The mono-azo dichroic dye compound according to claim 1, wherein Z is CN or indanone.
 9. The mono-azo dichroic dye compound according to claim 1, which is any one selected from the compounds represented by the following chemical formulae:


10. A composition for a polarizing plate, comprising: a liquid crystal compound; and the mono-azo dichroic dye compound of claim
 1. 11. A polarizing plate, which is a cured product of the composition of claim
 10. 12. The polarizing plate according to claim 11, wherein the polarizing plate has a dichroic ratio (D0) of 20-24.
 13. The polarizing plate according to claim 11, wherein the polarizing plate has a heat resistance (Δintensity) of 4% or less.
 14. The polarizing plate according to claim 11, wherein the polarizing plate has a photo-resistance (Δintensity) of 4% or less.
 15. An optical device comprising the polarizing plate of claim
 11. 